Error codes are used in a variety of signaling systems to detect and, in some cases, correct errors relating to data transmission and storage. The codes generally provide redundancy to the original data so that, when the data is encoded via a particular error code algorithm, a limited number of data errors may be identified and possibly corrected upon decoding. The redundant portions of the encoded data may take the form of checksums, parity bits, or the like, depending on the type of error code employed.
For memory systems that employ error codes, the overhead often employed with the encoding generally limits the effectiveness of the code to a single-bit error in a given word. As a result, only a certain number of hard errors, such as those caused by storage cell failures, may be acceptable for a given memory component before the component fails as a reliable device. The failures become even more costly when memory devices are assembled onto memory modules, and the modules discarded for failing to pass final testing.